Field Evaluation of Witczak and Hirsch Models for Predicting Dynamic Modulus of Hot-Mix Asphalt (With Discussion)

The Federal Highway Administration (FHWA) has been evaluating the Simple Performance Tester (SPT) in a field laboratory environment and preliminary findings lead to an investigation of whether the total amount of laboratory testing can be decreased, if appropriate theoretical methods for predicting hot mix performance characteristics are employed. Thus, dynamic modulus, |E*|, values were predicted using the Witczak and Hirsch Models for asphalt mixtures from five pavement construction sites across the United States. |E*| values predicted from equations were then compared to the values measured in the laboratory by the FHWA mobile asphalt laboratory (MATL) to evaluate the predictive capability of the Witczak and Hirsch models. |E*| master curves were generated and the Global Aging System proposed by Mirza and Witczak was evaluated using the |E*| measurements and predictions. Results indicate that both models provide reasonable predictions of dynamic modulus within the scope of this study. It was also found that the binder’s Useful Temperature Range (UTR) calculated by algebraically summing the high and the low continuous PG grade temperatures may be used to accurately predict the activation energy E sub A. The hot-mix shift factors may then be determined using the predicted E sub A and the Arrhenius shift factor equation. Recommendations are made for improvements in the Witczak and Hirsch predictive models. The National Cooperative Highway Research Program (NCHRP) 1-37A pavement design guide software was used to predict the performance of a trial conventional flexible pavement section. Both measured and predicted |E*| data from each site w used as inputs in the design guide software for a Level 1, Level 2, and Level 3 analysis. In general, the subtotal AC rutting results predicted by the design guide were found to be inconsistent at any Level of analysis with the magnitude of differences in the Superpave PG grades of asphalt binders used (from PG58-28 to PG70-22). Suggestions for refinement of the NCHRP 1-37A design guide models for characterizing asphalt materials are discussed.


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  • Accession Number: 01020729
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Mar 1 2006 7:50PM